1. Field of the Invention
The present invention relates to a dielectric resonator device used in a microwave band and a millimeter-wave band.
2. Description of the Related Art
Conventionally, there has been a demand for miniaturizing dielectric resonator devices such as filters, oscillators, or the like, which incorporate dielectric resonators. In response to the demand, a plane circuit type dielectric resonator device has been developed. For example, there is a "para-millimeter wave band pass filter equipped with a plane circuit type dielectric resonator", 1996, Institute of Electronics, Information and Communication Engineers General Meeting C-121, and a "plane circuit type dielectric resonator device" in Japanese Patent Application No. 9-101458.
FIGS. 14 and 15 show an example of a dielectric resonator device employed in the above patent application. FIG. 14 is an exploded perspective view of the device. In this figure, electrodes having three mutually opposing pairs of rectangular openings are disposed on each of both main surfaces of a dielectric plate 1. On the upper surface of an I/O substrate 7 are disposed microstrip lines 9 and 10 which are used as probes, and on substantially the entire lower surface of the same is formed a ground electrode. A single dielectric resonator device is formed by sequentially stacking a spacer 11, the dielectric plate 1, and a cover 6 on the I/O substrate 7. FIGS. 15A, 15B, and 15C respectively show an electromagnetic field distribution view of three resonators formed in the dielectric plate 1. FIG. 15A is a plan view of the dielectric plate 1; FIG. 15B is a sectional view of three electrode openings 4a, 4b, and 4c; and FIG. 15C is a sectional view in the narrow side direction of the dielectric plate 1. The rectangular electrode openings 4a, 4b, and 4c having a length L and a width W, which are mutually opposed having the dielectric plate 1 therebetween are formed at given gaps g. This arrangement permits formation of a dielectric resonator with a rectangular slot mode on each of the electrode openings 4a, 4b, and 4c, leading to formation of a filter having three-step resonators in the overall structure.
The conventional type of dielectric resonator device shown in FIGS. 14 and 15 is extremely miniaturized overall, since it is a plane circuit type device in which a resonator is formed in a dielectric plate. However, in the conventional type of device incorporating a dielectric resonator with a rectangular slot mode, for example, non-loading Q (hereinafter referred to as Q0) is not higher than that in a dielectric resonator with the TE01.delta. mode, since conductor loss of electrodes formed on both main surfaces of the dielectric plate is large. This causes a problem such as increase in insertion loss when a band pass filter is formed.
In order to increase Q0 of the resonator, it is effective to make the width of the resonator (the width W of the electrode opening) longer than the length of the same (the length L of the electrode opening). In this case, however, the resonant frequency of a mode (where the directional relationship between the width and length of the electrode opening is reversed), in which the electric field direction is orthogonal to a basic resonant mode, is close to a frequency of a basic mode, resulting in degradation of spurious characteristics.
In addition, in the conventional type of rectangular slot mode resonator, there are great changes in filter characteristics with respect to changes in structural dimensions of the length L and gap g of the resonator. This leads to decrease in production efficiency.
Furthermore, in this conventional type of device, adjustment of the resonant frequency performed by giving perturbation to the magnetic field and the electric field also decreases production efficiency, since control in adjustment is difficult due to great perturbation quantity.